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Chemical Engineering 301 0 Lecture Notes Chapters 1-2. Introduction and First Law Chapter 1. Introduction. Syllabus. Pass out and discuss. Web. Indicate location of syllabus and course materials on the World Wide Web (http://www.che.wsu.edu - then link through "faculty" to my home page, then through "courses" to this course). Scope of Thermodynamics. relate changes in the equilibrium state of a system to interactions between the system and its surroundings determine the efficiencies of alternative processes to effect a given change in state, with respect to the resources available calculate equilibrium states for systems involving multiple phases and chemical reactions measurement, estimation, and correlation of thermodynamic properties Basic Relations. First law: E t Q W E ( flow) E ( gen) Q Second law: S t S ( flow) S ( gen) T Phase equilibrium relations: fi fi fi Chemical reaction equilibrium: i fi RT ln K G o K fi The Devil is in the Details. simplification of general thermodynamics relations to apply to a real, complex problem combination of relations and setting up a solution scheme determination of relationships of internal energies, entropies, and fugacities to measurable properties (T, P, composition, density, etc.) for real fluids and solids understanding the use of thermodynamic tables, charts, and equations - representing measured properties, theoretical estimations, and empirical correlations estimation of the accuracy of the calculated results First Assignments. 1. Get on the Web and find syllabus, information on teams, and class notes. 2. Read Chapters 1 and 2 in the text. Basic Concepts. A list of basic definitions can be found at the end of the syllabus. Concepts which you should understand from previous courses: system surroundings system boundaries temperature pressure work heat material balance energy balance Temperature - the property which tells us whether systems are in thermal equilibrium, i.e., no heat transfer if two bodies at the same temperature are brought into thermal contact. Heat - energy in transition across the boundaries of a system due to a temperature difference. Work - energy in transition across the boundaries of a system due to a driving force other than temperature, and not associated with mass flowing across the boundaries. Work in moving the system boundaries against an opposing pressure. V dW Fdl PAd PdV A Other types of work: shaft work, electrical work, surface spreading, etc. Types of energy: kinetic, potential, internal. mu 2 E t mgz U t 2 State and path functions: Discuss intensive and extensive properties (t means total). State - unique set of intensive properties specifies the intensive state - the extent of the system (total mass) must also be specified to completely specify the overall state of a system. State functions - depend only on the state of a system, and not its past history - such as U, H, S, etc. - when differential changes in state functions are integrated over a finite accounting period, differences are obtained: dU U 2 U 1 . t t t Path functions - related to changes in the state of a system, and depend on how these changes take place - such as Q, W, E(flow), E(gen), etc. - when differential amounts of these functions are integrated over a finite accounting period, total amounts are obtained: dQ Q . Process - change in the state of a system - cyclic processes return to the same initial state. Chapter 2. The First Law of Thermodynamics General Differential Form (Differential Accounting Period). dE t dQ dW dE ( flow) dE ( gen) General Integrated Form (Finite Accounting Period). E2 E1t Q W E ( flow) E ( gen) t Some simplifications: steady-state: Et2 - Et1 = 0 adiabatic system: Q = 0 closed system: E(flow) = 0 negligible kinetic and potential energies: Et = Ut no reactions or other sources or sinks: E(gen) = 0 isolated system: Q, W, E(flow) = 0 Batch Process with No Generation. This is a closed system, with negligible kinetic and potential energy changes. U 2 U 1t Q W t U t Q W Note that the change (the on the left-hand side of this equation) is relative to time, i.e., between the beginning and end of the accounting period. Chemical reactions can be included in this equation by including U of reaction in the Ut term. If the batch process is carried out at constant pressure, then there will be a work term. W PV t H t Q Ws where the shaft work term represents any other work that might be introduced. Steady-State Flow Process with No Generation. See Fig. 2.7, p. 52, as an example. 0 Q W E ( flow) W Ws PV1 P2V2 Ws PV 1 mu 2 E ( flow) E 1 E 2 E U t mgz 2 mu 2 mu 2 0 Q Ws PV U t mgz Q Ws H t mgz 2 2 Rewriting, with the last term on the left-hand side, we get t mu 2 H mgz Q Ws 2 Note that the change in this equation is between positions (cross sections 1 and 2), rather than time. If there is only one stream flowing in and one stream flowing out, this equation can be written per unit mass of fluid flowing through the system: u2 H gz Q Ws 2 where Q and Ws are the heat and shaft work per unit mass. This is Eq 2.32, p. 51. In many applications, the kinetic and potential energy changes are small, and these terms can be dropped from the LHS to get Eq 2.33 in the text. General Form - Expanded. E2 E1t Q W E ( flow) E ( gen) t t mu2 mu2 mu2 mu2 U mgz U t mgz Q Ws H t mgz H t mgz E ( gen) 2 2 2 1 2 in 2 out Work Example Problems. Example Problem 2.16 on p. 54 - use as a group exercise: 1. What is the basis used by the author in applying the 1st law? What is the accounting period? 2. gc is a units conversion factor. What are its units? 3. Where are the steam tables? Find the inlet and outlet conditions. 4. What would the final T be if Q=0? Equilibrium. a state of absolute rest no tendency to change state no processes no fluxes of energy, mass, or momentum no temperature, pressure, or concentration gradients thermal, mechanical, and chemical equilibrium phase and chemical reation equilibrium The Phase Rule. phase - a homogeneous region with uniform intensive properties at equilibrium - may be a liquid, vapor, or solid - may be continuous or discontinuous (dispersed) degrees of freedom (F) = number of intensive variables that must be specified to fix the state of a system phase equilibrium variables = T, P, compositions of all N components (in all phases) Phase Rule (applies at equilibrium): If there are no chemical reactions involved, F N 2 If there are r independent chemical reactions at equilibrium (see p. 591), F N 2 r Reversible Processes. reversible process - can be reversed at any time by an infinitesimal change in the driving force Can you describe the following? 1. reversible expansion (work) in a piston and cylinder 2. reversible heat transfer between a solid and a bath reversible work dW PdV Reversible processes in closed systems - heat capacities. U H Definitions: CV CP T V TP 1. Constant volume process. dQ dU t ndU nCV dT T2 Q U nU n CV dT t T1 2. Constant pressure process. dQ dU t PdV t dU t dPV t dH t ndH nCP dT T2 Q H nH n CP dT t T1